An exemplary method of molding a thermosetting resin (hereinafter may be simply referred to as resin) injects the resin into a mold and heats the mold. A known resin injection device used for this molding method is a gate valve configured to open and close a resin injection hole by moving a gate valve pin. This gate valve is cleaned at regular intervals, in order to avoid potential troubles caused by an increase in viscosity of the resin or curing of the resin retained inside of the gate valve.
For example, Patent Document 1 specified below describes a gate valve that can be cleaned. This gate valve includes a gate valve pin configured to open and close a resin injection hole and a discharge flow path for a cleaning liquid formed by a space between a casing and the gate valve pin of the gate valve. A resin supply flow path is formed inside of the gate valve pin. The supply flow path is made to communicate with outside of the gate valve pin via an opening formed in the vicinity of a front end section on the injection hole side of the gate valve pin. The gate valve pin partly has a first convex protruded from a side surface thereof to have a larger outer diameter. The casing has a second convex protruded from an inner surface of receiving the gate valve pin toward the gate valve pin to narrow the diameter of the discharge flow path above the first convex. The gate valve of this configuration operates as described below.
Moving the gate valve pin upward opens the injection hole. In this state, the first convex comes into contact with the second convex to block the discharge flow path in the middle thereof. In this state, when the resin is supplied through the supply flow path, the resin is flowed through the supply flow path inside of the gate valve pin into the injection hole via the opening. When the gate valve pin is moved downward, the injection hole is closed by an end of the gate valve pin. The first convex is accordingly not in contact with the second convex, so that the blocked discharge flow path is opened. The discharge flow path is made to communicate with the supply flow path via the opening of the gate valve pin. In this state, when the cleaning liquid is supplied through the supply flow path, the cleaning liquid cleans the flow passage of the resin and is discharged through the discharge flow path. As clearly understood from the above description, in the gate valve of Patent Document 1, when one of the injection hole and the discharge flow path is opened, the other is always closed.